Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$227.77	8.599%	$247.3559	$247.36	$247.35	$247.40
Purchase #2	$239.52	4.714%	$250.811	$250.81	$250.80	$250.80
Purchase #3	$176.96	13.222%	$200.3577	$200.36	$200.35	$200.40
Purchase #4	$12.45	6.543%	$13.2646	$13.26	$13.25	$13.30
Purchase #5	$208.59	8.862%	$227.0752	$227.08	$227.10	$227.10
Purchase #6	$233.90	10.418%	$258.2677	$258.27	$258.25	$258.30
Purchase #7	$116.32	13.143%	$131.6079	$131.61	$131.60	$131.60
7 purchase totals =	$1,215.51		$1,328.7400	$1,328.75	$1,328.70	$1,328.90